Self-supporting run-flat tires have been commercialized for many years. The primary characteristic of such tires is an increase in the cross-sectional thickness of the sidewalls to strengthen the sidewalls. These tires, when operated in the uninflated condition, place the reinforcing sidewall inserts in compression. Due to the large amounts of rubber required to stiffen the sidewall members, heat build-up is a major factor in tire failure. This is especially true when the tire is operated for prolonged periods at high speeds in the uninflated condition.
U.S. Pat. No. 5,368,082 teaches the employment of special sidewall inserts to improve stiffness. Approximately six additional pounds of weight per tire are required to support an 800 lb load in an uninflated tire. The earliest commercial use of such runflat tires were used on a high performance vehicle and had a very low aspect ratio. The required supported weight for an uninflated luxury car tire, having an aspect ratios in the 55% to 65% range or greater, approximates 1400 lbs load. Such higher loads for larger run-flat tires meant that the sidewalls and overall tire had to be stiffened to the point of compromising ride. Luxury vehicle owners simply will not sacrifice ride quality for runflat capability. The engineering requirements have been to provide a runflat tire with no loss in ride or performance. In the very stiff suspension performance type vehicle the ability to provide such a tire was comparatively easy when compared to luxury sedans with a softer ride characteristic. Light truck and sport utility vehicles, although not as sensitive to ride performance, provide a runflat tire market that ranges from accepting a stiffer ride to demanding the softer luxury type ride.
It is thus desired to provide a novel run on flat tire design that is a “soft” run on flat design, so that no compromise in comfort is required while having the same chassis loading as a regular pneumatic tire.